1. Field of the Invention
This invention relates generally to animal litter compositions and methods therefor and, more particularly, to novel animal litter compositions containing silica gel and an absorbant material and methods therefor. The new compositions can be characterized as being sorptive for moisture and undesirable odors.
2. Description of the Related Art
Although a number of absorbant substances can function as animal litter, including recycled newspaper, paper sludge, corn cob granules, rice hulls, peanut hulls, sunflower hulls, alfalfa, cedar, sawdust, and litters made from other organic plant materials, clay is the most commonly used material for litter-box fillers. Typical clays used are calcium and sodium montmorillonites (including sodium bentonite), attapulgites, kaolins, and opal clay mixtures. All of these absorb animal urine and help to cover the fecal waste and decrease odors.
Two types of clays have been used as animal litter. The gelling clays, such as sodium bentonite, form a clump when contacted with animal urine and can, therefore, be scooped out to prevent odor build up. These have been referred to as clumping litters which have grown in popularity to account for over half of all litter sales. Litters made from non-gelling clays, sometimes referred to as non-clumping litters, absorb the urine, but only the solid fecal matter can be scooped out. The non-clumping litters do not last long and are completely changed with fresh material when the odor becomes too strong. This is also true for litters made from materials other than clay.
One disadvantage of clays, and most other materials used for animal litter, is that the odor is not effectively controlled by the litter material. Odors produced from animal urine and fecal materials include ammonia as well as a variety of organic sulfur materials. These typical odorous gases associated with animal waste are not absorbed into clay litter materials, but are adsorbed onto the surface. As a result, the odorous gases volatilize back into the air creating an objectionable odor problem.
Various approaches have been tried to diminish the odor emanating from litter. In one such approach, fragrances have been used to mask odors. U.S. Pat. No. 4,020,156 to Murray et al. discloses fragrance-releasing crystal beads as agents for controlling malodors in pet litter. U.S. Pat. No. 4,085,704 to Frazier discloses a vehicle impregnated with an odor control agent such as a perfume, flavor, fragrance or essence oil, for mixing with an absorbant litter material. The '704 patent disclosed the use of silica gel as one possible carrier for the odor controlling agent, however, this reference neither disclosed nor suggested the use of the silica gel or any other carrier substance in absence of the odor controlling agent nor did this reference suggest the use of the carrier substances for anything more than a vehicle of the odor controlling agent. In that regard, although many substances, including clay litters, can contribute at least some odor controlling activity by absorbing the odorous substances, it is likely that the prior impregnation of the carrier with the odor controlling agent would have precluded the carrier from having any meaningful activity in absorbing the odorous substances from animal urine and feces. Thus, while the use of odor masking agents can be beneficial, their effectiveness is limited by virtue of their acting to mask the odors rather than to eliminate the odors.
Others have used germicides to inhibit odor causing microorganisms. For example, U.S. Pat. No. 4,607,594 disclosed the use of a quaternary amine germicide in a litter composition. U.S. Pat. No. 4,930,443 to Lowe et al. discloses an animal litter which includes a bacterial and fungal growth inhibitor, polyvinylpyrrolidone iodine complex, which is dissolved in water and sprayed onto the litter. Furthermore, various chemicals have also been used to react with the odor-causing substances. U.S. Pat. No. 4,607,594 to Thacker discloses an animal litter using buffering agents such as a carbonate, a bicarbonate or hydrogen phosphate. U.S. Pat. No. 5,005,520 to Michael discloses the use of an oxidizing additive, such as sodium perborate in animal litter. Similarly Reddy et al. disclosed the addition of urease negative bacteria to clay pet litter to inhibit the growth of urease positive bacteria, thereby retarding formation of ammonia and other obnoxious odors (U.S. Pat. Nos. 5,507,250 and 5,634,4310). None of these approaches, however, have been effective in preventing the development of odorous substances from animal litter containing animal waste products.
In another approach, animal litter can be made of substances which exert a sorptive effect on odorous gases. For example, U.S. Pat. No. 6,106,738 to Woo et al. discloses spraying a cyclodextrin solution onto cat litter to absorb malodor. Similarly, zeolites have been used in cat litters to adsorb odorous gases. Cat litters which are 100% zeolite are currently marketed in the U.S. Alternatively, zeolites can be added to clay litters to control odor. For example, U.S. Pat. No. 4,437,429 to Goldstein et al. discloses the addition of zeolites to the clay component of animal litter to control odors from the litter. Zeolites are, however, significantly more expensive than clay and, as a result, litters made from zeolite tend to be more expensive than clay litters.
A number of substances have been used to eliminate odors due to organic molecular species in air filtering systems. Among these substances, silica gel has been used as a solid adsorbent for removing odors from the air. (see for example, U.S. Pat. Nos. 4,795,482, 4,604,110, 4,534,775 and 4,517,308). In that regard, silica gel has been mentioned as one possible odor absorbing material for use in an air filter component of a litter box assembly to remove undesirable odors. Thus, U.S. Pat. No. 5,044,325 to Miksitz discloses an animal litter box which includes a litter box tray and housing and an exhaust fan coupled with an odor absorbing filter assembly to deodorize the air before venting the air from the litter box.
Recently, silica gel has been employed as a litter box filler (see U.S. Pat. No. 5,970,915). The silica gel used was macroporous silica gel which was reported to effectively eliminate odors in addition to absorbing moisture from the urine. A significant problem with the use of silica gel as an animal litter is that silica gel is substantially more costly than clay litter box fillers. Although 100% silica gel has been used as a litter to absorb odors, silica gel has not been used as a component of a litter composition in combination with clay litter because it has not heretofore been appreciated that silica gel could serve as an effective odor control agent when mixed with a clay litter. Thus there remains a continuing need for new animal litter compositions which control odors in addition to absorbing liquid animal waste materials.